Volumetric measuring apparatus



Jam 19, 1954 F. M. POOLE ET AL voLuMETRIc MEASURING APPARATUS 11 sheets-sheet 1 Filed Deo. 22, 194'7 Jln- 19, 1954 F. M. PooLE E'r AL VOLMETRIC MEASURING APPARATUS 1i sheets-sheet 2 Filed Dec. 22, 1947 llflcszA. 97

Jam 19, 1954 F. M. POOLE ETAL VOLUMETRIC MEASURING APPARATUS 11 Sheets-Sheet 4 Filed Dec.y 22. Ai947 www IIb-:|2521- M. Pan-2.

(3f/Dawg LM-QL.

Jan- 19, 1954 F. M. POOLE ETAL VOLUMETRIC MEASURING APPARATUS 11 Sheets-Sheet 5 Filed Deo. 22, 1947 n mg J 1 WU. 1

Foa/G29 M750-ren.

Jan. 19, 1954 F, M, POOLE ETAL 2,666,326

VOLUMETR-IC MEASURING APPARATUS Filed Dec. 22, 1947 11 Sheets-Sheet 6 Jan. 19, 1954 F. M. POOLE ET AL 2,666,326

voLUMETRIc MEASURING APPARATUS Filed Dec. 22, 1947 11 Sheets-Sheet 7 FIGS.

MASTER FREQUENCY O TOLERANCE INDICATOR AND COUNTER E CONTROL EQUIPMENT UNIT G SAMPLE FREQUENCY COUNTER I;-

Jan. 19, 1954 F. M. POOLE ETAL VOLUMETRIC MEASURING APPARATUS 11 Sheets-Sheet 8 Filed Deo. 22, 1947 Jan. 19, 1954 Filed Dec. 22, 1947 FIGLIO.l

. 11 Sheets-Sheet 9 Jam 19, 1954 A F. M. POOLE ET AL 2,666,326

VOLUMETRIC MEASURING APPARATUS` Filed Dec. 22, 1947 11 Sheets-Sheet lO FREQUENQCY METER Fna M. mwen,

Jam 19, -1954 F. M. POOLE l-:T AL

voLuMETRIc MEASURING APPARATUS 11 Sheets-Sheet ll Filed Dec. 22, 1947k FIG. I4.

a4 f@ .m E mw 7 ffm m w wo m 7 2 7 7 6 8 6 m M ,L

f Patented Jan. 19, 1954 '2,666,326

" fr mi;

ng we yk Wires t which Roman cause the air within each cavity to resonate at its natural frequency of resonance.

An electroacoustic transducer or loudspeaker It is mounted on closure within a housing I2 to cause vibration of the air in throat 6 and resonance of the air in the master cavity I. A receiver or microphone I4 is carried by the closure 5 in acoustic communication with the master cavity. 'Acoustic communication may also be attained, for example, by separately mounting the microphone against the outside of the body containing the cavity. That is, the microphone need not be mounted on the4 closure member to be in acoustic communication with the cavity. The electrical output of microphone I4 is coupled by wires I6 to the input'of an amplifier D, hereinafter designated as the master amplifier. One output of this amplifier -is coupled to the transducer I0 as by wires I8 to vform a closed oscillatory circuit.

Similarly, an electroacoustic transducer or loudspeaker is mounted on closure 1 within a housing 22 to cause vibration of the air in throat 8 and resonance of the air yin'sample cavity 4. A microphone 24 is carried by closure 'I in acoustic communication with the master cavity. The electrical output of microphone 24 is coupled as by wires 26 to the input of an amplier A, hereinafter referred to as the sample amplifier. One output of the sample amplifier is.

coupled to the transducer as by wires'28 to form a closed oscillatory circuit.

A second output of the master amplifier D is coupled to the input of a frequency counter E, hereinafter referred to as the master frequency counter, by wires 38. Similarly, a second output of sample amplifier A is coupled to the input of a frequency counter F, hereinafter referred to as theV sample frequency counter, by wires 32. The function of these frequency counters is to convert the A. C. signals received from the respective amplifiers Vto D. C. voltages, the potentials of which are functions of the frequencies of the respective A. C. signals. The

C. Voutputs of the master and sample frerespectvely, to an indicato'r'unit X, such as a galvanometer, in such manner'that the indicator functions in response to and indicates the difference in the D. C. voltages put into it from the frequency counters. Thus indicator X measures the difference in volumes.

The operation of the apparatusv generally is as follows:

Any casual ambient sound received by the microphones I4 and 24 is converted thereby into electrical signals. These signals are fed to the master and sample amplifiers, respectively.

The signal received by the master amplifier D is amplified and fed to the transducer I0 which converts it into vibrating acoustic energy. This energy is converted by microphone I4 to an electrical signal, which is received by the master amplifier D, amplified, and fed to the transducer I0. The oscillations in the closed oscillatory circuit quickly 'build up to the point Where the air in the master cavity is caused to oscillate at its natural resonant frequency as determined by the volume of the cavity andv the characteristics of the throat 6.

Similarly, the electrical signal received by the sample amplifier A is amplified and fed to the transducer 20 which converts it to acoustic energy. This energy is converted by microphone 24 to an electrical signal, which is received by the Y transducer 20.

quency counters are coupled by wires 34 and 36,

4 sample amplifier, amplified, and fed to th The oscillations in the closed oscillatory circuit quickly build up to the point where the air in the sample cavity is caused to oscillate at its natural resonant frequency as determined by the volume of the sample cavity and the characteristics of the throat 8.

The master and sample amplifiers D and A have components for maintaining the amplitude of the electrical signals therethrough substantially constant. Thus, the sonic oscillation of the air within each of the master and standard cavities is maintained at a, substantially constant amplitude, and at a frequency which is a function of thevolume of the respective cavity. The output of the master amplifier, an A. C. signal having a frequency corresponding to the resonant frequencyV of oscillation of the air in the master cavity and thus corresponding to the volume of the cavity, is` converted by the master frequency counter E to a D. C. voltage, the potential of which is a measure of the volume of the master cavity. The output of the sample amplifier, an A. C. signal having e, frequency corresponding to the resonant frequency of the air in the sample cavity and thus corresopnding to the volume of the sample cavity, is converted by the sample frequency counter F to a D. C. voltage, the potential of which is a measure of the Volume of the sample cavity. The difference between these two potentials is indicated by the meter X as an indication of the difference between the volume of the sample cavity and the volume of the master cavity. The meter may be calibrated in terms of volume to give direct volume readings.

The closed master and sample cavities may be located closely adjacent to one another so as to be equally affected by changes in ambient temperature and/or humidity. Thus, the apparatus is inherently self-compensating so far as ambient temperature and humidity effects are concerned. Y

Figs. 2 8 illustrate in detail an embodiment of the invention particularly for rapidly measuring or testing the volumes of the cavities in the head block of an internal combustion engine to determine whether the volumes are within required tolerance limits.V This embodiment is shown in Fig. 2 to have a foundation 9 upon which a base member II is fixed by bolts I3. The base member is centrally formed with a depending cylindrical wall I5 open at its upper and lower ends. Within the wall I5 is a cylinder I'I having a flange I9 at its upper end fixed to the base member 4I by bolts. The lower endsof both cylindrical wall I5 and cylinder I1 are closed and sealed by a closure plate 2l fixed thereto by bolts ,23. The flange I9 closes the upper end of wall. I5 around cylinder I'I. A piston 25 is slidable in the latter.

The space between Wall I5 Vand cylinder II forms a reservoir. Compressed air may be supplied to the upper Vend kof the reservoir through a pipe 21 and an inlet 29. j The reservoir contains fluid 3| and is in communication with the lower end of cylinder I'I through a pipe 33 and fittings 35. The arrangement is such that when compressed air is admitted to thereservoir, the reservoir fluid is forced into thel cylinder Il to raise the piston 25 from its lowered position of Fig. 2. When pressure is released, 'the piston will descend. f

A Work-holding table 39 is 4fixed upon the upper end of piston 25 by Ybolts 4I. The table is guided for vertical movement by guide posts 43 and 45 (potentiometer |91). Assuming for this initial state that tube 20| is conducting and the potential just impressed on control grid |93 is a negative one, the tube will conduct less (or possibly cut ofi if the negative potential is great enough) causing a decrease of current through cathode bias resistor 203, by-passed with cathode condenser 205, and will thereby cause a decrease in current through plate load resistor |99 and decoupling resistor 201 (by-passed with decoupling condenser 299). The screen grid 2|| of tube 20| has impressed on it a constant potential supplied by a bleeder network consisting of resistor 2|3 and resistor 2|5, both by-passed by condenser 2|1. The decrease in plate current through plate load resistor |99 results in an increase 1n potential at the top of resistor |99. The latter is coupled to control grid 2|9 of a vacuum tube 223 through coupling condenser 208 and iinpresses the increase in potential across the grid resistor 22| for tube 223.

Assuming that tube 223 is not in a saturated condition (it may be very near cutoff), this 1ncrease in potential will cause tube 223 to conduct to a greater extent and thereby'. cause a greater flow of current through cathode bias resistor 225 (by-passed by cathode condenser 221), primary winding 229 of a transformer 230, and decoupling resistor 23| (by-passed by decoupling condenser 233). This change in current flow will cause a current to flow in secondary winding 235 of the transformer 235 which is coupled to energize transducer 89, and thus causes the slug of air in the respective throat opening 239 to oscillate. The movement of this slug of air will cause compression or expansion of the air in master cavity 5|. Any compression or expansion of air in cavity 5| will aiect the microphone 99 and cause a change in the flow of current through the primary winding |53 of transformer |65.

Due to the predeterminately arranged inherent electrical characteristics of the circuit of the master amplifier unit D and the feedback arrangement between transducer 89 and microonce the electrical oscillations are started by a f casual noise as mentioned, they will be sustained by the feedback system employed and both acoustic and electrical oscillation will continue, providing that the potentiometer |69, potentiometer |91, and variable condenser |95 are properly adjusted, as will be later described.

VThe frequency of the electrical and acoustic oscillations is then the same and is dependent upon the volume of the master cavity 5| as mentioned previously.

The operation, construction, circuits, and all component parts of the sample amplifier unit A are respectively identical with those of the master amplifier unit D and are therefore identically indexed, as shown. The sample amplier A, as will be shown later, can be switched easily and rapidly from one to another of the cavities 53 by means of the stepper switch B v(Fig. 6).

During operation the wave-forms on the control grids l1|, |93 and 2|9 are substantially sinusoidal 'and the tubes |13, 29| and 223 will operate between the limits of cutoff and saturation. Tube |13 is biased by cathode bias resistor |15 and cathode condenser |11, the value of the latter being chosen to assure no degeneration.

Tube 20| is biased by cathode bias resistor 203 and cathode condenser 205, the value of the latter being chosen to assure no degeneration. Tube 223 is biased by cathode bias resistor 225 and cathode condenser 221, the value of the latter being chosen to assure no degeneration. The source of power for tubes |13, 20| and 223 is power supply ||9. Y

To prevent blocking due to overloading, and to maintain the acoustic and electric oscillations at a substantially constant amplitude, both the master and sample amplifiers are provided with an automatic volume control circuit. These circuits are fed respectively from secondaries 25S of the transformers 230 in the respective amplifiers. Both automatic volume control circuits are identical and are identically indexed in Figs. 6 and 7. Each circuit includes the secondary 24| of transformer 230 coupled to apply a potential acrossY plates 243 and 245 of an automatic volume control tube 261 of the duo-diode type. This potential results from the current induced in secondary 22| by the sinusoidal current developed in the primary 229 of transformer 235. The plates 2653 and 245 generally are diiierent in polarity.

The cathode 249 of tube 241 is at a potential (of +20 volts for example) which is supplied by power supply 238. When the master oscillator D, and sample oscillator A, start to operate they will tend to drive themselves to a point where one of the tubes |13, 20 or 223 becomes saturated or cut oir". However, as the output of tube 223 increases over a certain value causing the potential acrcss secondary winding 235 to exceed 20 volts, tube 241 will conduct, causing a iiow of current through load resistor 25|. The potential across load resistor 25|, caused by the aforementioned flow of current, is impressed upon control grid |93 through line |31, resistor 253, potentiometer |91, and variable condenser |95. This variation in potential will automatically bias tube 29|, decreasing its gain as the potential across secondary winding 24| increases. This system tends to keep the output of tube 223 at a constant level in amplitude. Decoupling resistor 253 and decoupling condenser 255 prevent any undesired load Variations on tube 241 from being reflected along line |31 to control grid |93.

The output of a secondary winding 251 of transformer 23|), a sinusoidal type wave, substantially constant in amplitude, is impressed on control grids 259 and 25| of two vacuum tubes 293 and 265 (Fig. 8) through two grid bias resistors 251 and 268. The tubes 233 and 295 are connected in a modied push-push circuit, and the potentials on control grids 259 and 29| will, therefore, at any instant, generally be opposite in polarity.

Starting at an instant when the potential of control grid 259 is increasing positively, current will be drawn through cathode resistor 21|, causing an increasing positive potential at the top of this resistor 21|, which will increase the potential of the top plate of a condenser 295 and a plate 213 of a duo-diode tube 233. Increasing current will thus iiow through a resistor 235 (in unit E) or 30| (in unit F), increasing the potential at cathode 281 of tube 283.

Taking another instant, this time when the potential of control grid 2H of tube 205 is increasing positively, the potential at the bottom of a cathode resistor 259 is increasing positively due to the increasing current which is being drawn through it by the greater conduction of adiutsd until-theatres shifts r1211.10-a25.-;V inereasinapptential iss-impressed y. uponplate-215oi tube.l2f 8t.3 'and .tli'ebottomjplate of. condenser, 25.5. i rlliis` increasing, potential-g at plate.2;155Will-causethepotentiallacross there'sistor 285.. (in. the counter. E1).x 011.351., (inthe-.counter F) to increase.

The valuesof. the .circuihconiponentsareso chosen as to keep.thedischargatimes.ot:coupling condensers 294 and .2 5.31sunstantially-greaterltlian .that oi. condenser 255. The-potential-acrosslreesister. 285 or Se! is. causedto increase withann.- creaseV in input. frequency tothe controllgrids'g and 23| andtoce'crease vvithsadecreaseininputV frequency to. control. grids.. 259.and'f 2:61a Therefore, as thev inputV sinusoidal .Wave impressed on control grids 9and-,2Q6Lis sulos'tantiallyfcons tant .in amplitude, the. potential... across resistor 285.0136! is dependentonlyont-he natural resonant frequency of .the testedcavities, .the potentials rising with. anincrease infreauency, and decreasing with a vdecrease.in..frenuency.

. Resistor` .291 is.. an. additionalfcathodebias resistor used incomruon bytubes liandh'l'm power supply- 29S is theL sourcejotpovver, for.. tubes A253, 255 and 283. Thejcircuit..operation,,con struction. and, all component. partsl ofthe,- master frequency counter.` E and the.. sample-y irequency counter F areidentical.,

. Referring newA morev particularly to the tolerance. indicator.. and: control. eqiiiloment.v unit. G, li'ig.y 8, reference. numeral' 139.indicatesl a .three position (.manual` .fo. and. automatic.) switchhav-ing three sets of contacts 315.51, and I). Cnly contacts-fUil-l arev closed,..inthe".i position, contactsl5llfandf 313 remaining open.

The D. C. potentials of vresistors"2`i35fandlll be compared by positioningv svvitch-y i159. in. its off position..thus-connecting, the potential acrosswresistor. Zittil in opp'ositian.y to the potential lacross resistor 3cithrough contacts-Miliof 'switch 13s,. contacts 35|.andoeezotarelay entre (which ris energized inthe foft positionof switch. (39) and throughf a meter. (amicrofarnpere.. indi.- cating. galvanometerf), and a.: potentiometer `3.13.

With the 'switch '1.33. in .the yeti-3'" 'pfc'isi'tionfl and a contactv arm. VCA ot; stepper ,fsvvitclnBi` aligned ori-contacts liti, 7.151,.8.6L,.and-.Stilv (Eie), it-.Will be noted that microphoneilt. master; cavity: 5I, and transducerl 8.3. allare,commontoloothmaster a-mplier. `D A and sample amplifier through con,- 'tacts Gand H- liehmfzl. (whith. belebt-led vstandardize' isy now powered-loyvpovven supply 323* (Eig: 8) throughcontacttL, and. isthereiore lighted. Therefore, if: every-thing is Afunctioning properly, thepotentialfatfthertop of. resisten 2.85 andfat the top of; resistor 3m utillfheequal. and. no current will.. ow through-'.nieterf-i, poten.- .tiometer 313;. or;- the-meter.v 3&5 (any adjustable #Sensitrolii type; galvanometer with... magnetic contacts SIi'LaIiriV 3119)@v vlhiclju-.is connectedto.- getherwvith a potentiometer 3.15 inlparallelwith meter- 303. f 'N The.- electronic. adj ustmentss. may now. be; made follorvszf These adjustments should. h egmade when arms 3H. andi 3t2,-of. potentionie'els 13 .and 315 respectivelylere, at the eXtnen/iev left l(minimum -resistance),., will2 give maximum :sensitivity to metersA 3&3 and 305z te tiometers L69.; arev adjusteiifethere is; an Y scale. reading on. meter. ,3Q ,toi atp meter 322i gives the miriirni'irnt.pl1 y de ectiornV adiustmentxisfratelyt y n Botentiometers 5,917 and varia-hieL con-dansers L55! in each .ot the, ampliiier circuitst A, and.: Dfare `lowingunits:,a. relay coil 32.5 oithestepperis input. Siena1-through master.. .amplifier D., .and sampleamplifier. A) :areV properlfor.Y oscillation around. through the. acousticalr path, yanc l.un."ti l.. he electronic characteristics.. of, the unitD -and the unit A. become such. that,r there... is .f thecorrect phaserelationshipbetween the period kci the master cavity 5l and the .phase shifts through the ,master amplier Dand thesampvl-e amplifier A.. This .Will give full amplicaticnto anycasual sound initially picked up by any. ofthelmiorophones 99A; IM, |03, |05, ILl'e,ani |1IZLfThen micro-ampere. indicating galvanometer. 310.3 and galvanoineter. type rel-ay.. 3115. bothshouldmow read .exactly mitlscale which indicatesljzerolpo.- tential difference. between y, the.v potentials, across resistors 235..and.31|..

Potentiometer 3&3 may then be adjustedso that it WilLgive any desiredscale.. reading: of meter.. Sil-'vperdifference in volumes.. -Pctenftiometer 3I5 adjusts the sensitivity oimeterg varying the tolerance` limits-of volume, ldie'rence at which either lofbitstwo magneticcontact] or.3'09iwill. be contactedbyacontact arm 3.2.4..

A` power. supply 3.23tsupplies power. to the/fol#l Ch unit. B. (Fig. 6,), a. reset-.coi1..3,2. of.. meter o 5l., a relay coil 325, arelay. 0011.331, arelay'coil, a relay4 coil 335, andlights [2J-,1.23, 1.25., 121,4 29 l3l,1|3,3, |35-, 3I'l,l 319... Y

To. ascertain the respective volumesof cavities 53 or their respective volume differences a'sgcomf pared. to. master. cavity 5-i,.the stepper switch unitllis-` providedl either.v automatically or. man..- uallytto connect/separately. andlin. sequence each of the sixV cavities tothelsample ampliiiepa. The master, cavity 5.1 remains connectedNl always to. master amplierD.

'Such manual operation maybe. accomplished as follows: l

With the. switch -I-.39jin.manl1a1 position` and contacts G, H; I and. Jlof arm. CA.aligned.over contacts l6l',.'16.1,. 8.5L and. 95.1,.1'espectively, the only relay coils activatedare relay ctzilsgiifY (Eig. 6) and`335` (Fig.l 8)..,.,and.the only. lightin opera;- tion islight' |21,l providing that all adjustments previously mentionedare. correctly made.

When in. tl'emanual. position,` switch.- E has contacts '351,.closed and contacts, 3.13.` ano; .alli open. In the foiif position, sWit-chfl-Ifil, has'fonly contacts 40j closed.

As relay coil. 5F15 vis energized Whenswitchi. i is in .manual position,- its actionfvvfill-nowbetiescribed. It is energizedby power.- supply 323; (Eig. 8) through. contacts-f. I'and. J, wire 345; contact arm. 363, 'contact 3.33.3... and resistor 355i. Assoon as thispotentiallfrom power supply 3.2.3 irs-applied acrossvrelay coil 335.; .relay coil 3&5 Will movecontact. arms349 and lupward; connectingY con-- tact arm.35,l. tocontact 353.

When. switch. l is moved-.tothe pfffy posi..- tion', the.. contacts. 4.9.1 are clnsed. and. meters Siga and. 3.0.5 are.. them connected between. master frequency .counter E and;- .sample .frequency counter F.

f In. the ol position, contact/..351 o avv-itclfl i539 is.open, removing any potential'. from. relay., coi-1 325,.v When. switch, |59 i's-moved. .back again@ to Vthe .fmanual position. .relay-coilzii..isenergizeei switch Withcontaots evenlyfspaced.arounriitsipef riphery. By alternately moving switch |39 between oi and manua positions, coil 325 is alternatively energized through wire X, contacts 351 and wire IX from battery 323. This will cause contact arm CA to move in a clockwise direction and rest on contacts |4|, |43, |45, |41, |49 and |5| in the order mentioned.

Metersr303 and 305 are energized only when the arm CA is over any of the contacts 96|, 94|, 943, 945, 949 and 95| and switch |39 is in the 01T position. Thus, when the arm CA is moving between contacts, meters 303 and 305 are disconnected because such movement of arm CA occurs only when switch |39 is in manual position and when in this position contacts 40| are open and the circuit between resistors 285 and 30| is broken. Lights |35, |33, |3|, |29, |21 and |25 will each be lighted when contact I is contacting contacts 84|, 843, 845, 841, 849 and 85|, respectively.

Thus, by alternately moving the switch |39 between the manual and off positions arm CA is advanced in clockwise steps, testing in sequence each of the six cavities 53, the action of master amplifier D and the master frequency counter E providing a standard D. C. potential across resistor 285 which is compared in sequence to each of the six D. C. potentials which will be impressed across resistor 30| as a result of the action of sample `amplifier A and sample frequency counter F.

The arm CA may be returned to its starting position (aligned over contacts 959, 859, 159 and |59) by four more actuations of switch |39 between manual and off positions.

In the automatic position contacts 313 and 40| of switch |39 will be closed and contacts 351 will remain open.

Automatic operation is as follows: Assuming now that the contact arm CA is aligned on contacts |4|, 14|, 84| and 94| (Fig. 6), and switch |39 is in the automatic position, resistor 35| and condenser 341 (Fig. 8) will have impressed across them the potential of power supply 323, the connection being made through contacts 313 of switch |39. Condenser 341 will now charge through resistor 35| and after the time required for this charging, relay coil 333 will be activated, causing contact arms 363 and 365 to move upward. When contact arm 363 connects with contact 31|, power is supplied to relay coil 325, activating arm 359 and moving contact arm CA to a position aligned with contacts |43, 143, 843 and 943. The time required for condenser 341 to charge suiiiciently (approximately one second with the component values used) is the time required to test the sample cylinder head 53 below the transducer 13. Resistor 35| may be made variable or condenser 341 may be replaced with several various size condensers and a switch ,arrangement so that the time that any one cavity yis under test may be varied. Contact arm 355 ing the time when contact arm. CA is moving, Vv.the

'meters 303 and 305 will not be; activated.i

As soon as condenser 341 has discharged through resistor 361, contact arms 363 and 365 will move downward and the contact arm 363 will supply a potential through contact 369 to relay coil 335, causing contact arm 35| to be moved upwards, activating the meters 303 and 395 and thus completing one cycle of automatic operation. There is a small time delay required for relay coil 335 to reach the required potential to lift contact arms 349 and 35|. This delay is determined by the charging time of condenser 315 and resistor 311 and will allow the master frequency counter E and sample frequency counter F to settle down, and allow condensers 29| and 293 to discharge before operation starts again.

This cycle will be repeated until the contact arm CA is aligned on contacts |53, 153, 853 and 953. When this condition exists, no potential from power supply 323 is applied to relay coil 333 through wire VIII, but potential is applied directly from power supply 323 to relay coil 325 of the stepper switch B through a pair of contacts 31S and 38|. This is because there is no connection between contact 953 and line 345 as is the case with each of contacts 94|, 943, 945, 941, 949 and 95|. Arm 359 will be moved up and move Contact arm CA one step clockwise as coil 325 is energized, and this action will, as contact arm CA moves clockwise, `cause contact 319 to move away from contact 38|, (contact arm 383 being so constructed mechanically as to maintain an electrical connection between contacts 319 and 38| when arm 359 is in lowered position) when contact arm CA has moved suiiiciently clockwise. Contact 319 is insulated from pro- J'ection 385.

As there is now no delay circuit because relay 333 is not energized when arm CA is over contacts 953, 955, 951 or 9'59, the contact arm CA will move clockwise very rapidly due to the making and breaking of contactsr219 and 28| by projection 385 until it reaches a position aligned on contacts |59, 159, 859 and 959, the rest position, when light |23 is lighted, indicating that contact arm CA is in the rest position. When switch |39 is in the "automatic position and when arm CA is aligned over contacts 953, 955, 951 or 959 the meters 303 and 305 are deenergized. To start another cycle of "automatic operation, switch |39 must be first switched to off position and then returned to automatic" position. After the switch |39 is again in automatic position arm CA will move from a position over contact 959 to contact 96|. Arm CA will remain in that position until condenser 341 has charged suciently to energize coil 333. During this charging interval the operator has time to check the readings of meters 303 and 305 to de termine whether the apparatus is still standardized. The extra contacts made by arm CA, above, are for the purpose of taking care of eight-cylinder heads when desired. For the lat ter purpose additional resonance units and appropriate wiring are needed along the lines described herein regarding the six-cylinder set-up.

As contact arm CA rotates, lights |35, |33, |3'|,v

|29, |21, 25 Vwill be lighted when contact I is resting on contacts 84|, 843, 845, 841, B49 and respectively, and thus will indicate which of the sample six cylinder head cavities 53 is under test at any time.

Tolerance and volume indications are as follows: If we assume that the sample cavity 53 located under transducer 1| has a volume greater than the volume of the master cavity 5 I, and the ,accesso lmentioned ,volumesis greater than the...desired tolerancef the `following iaction will occur.:

The natural `frequency .of., res.onance `of .the sample cavity33 willhelower., andasa result the `potential across resistor` 33.1. will .be less .thanthe potential .across resistoro285. This..p0,tentia1.dif

ference .will .cause a current to iioWdoivn .through meters .303 and ,3.95 and. to the right.,through resistor-3 t5.' Meter 3113 will indicate'theamount lof volume difference inetheldesi-red .unitsrand the contact arm 32! of meter 305 will move .to .the right, vcontacting .contact ,3 0.1, and. .thus vconnecting relay coil Z33| -.to. power.-supply .323. This action will move..contact; arms 381 ,and.389 up,

andallow 11elay'arms38land 3.89 tomake;..con

tact respectively withcontactsil and,.39 3 f llhe connection .of contact ,arms .381 .and contact@ l .will supplyV power from powerlsupplyl323 .tolight Y.3l-9 which will therefore flight., indicating vl`.that

As the relay coil .335 iskept activated through contact .359, contact. arm35l :and lcontact @35.3, meters 3D3 and Bil'wwill remain mathe-@inuit between resistors .285' and-33|; thus indicating the exact amount of volume .difference fbetween the cavity 53 :under test andthe .master :cavity -If the sample `cavityct-.to -be-ftestedrhas `a ysmaller volume than the desired tolerance dimite will allow, the above action, .described .intnefpreceding two paragraphs, takes place with .onlythe vfollowing differences: Contact farrni .wiilconneet to Contact 339., `instead :of contactilmnd will activate relay -coil 329 instead of relayucoil 33|, This results in contact arm 49.3 heingconnested to Contact 4il5yand pewer'willrbecsupplied to light 3H, indicatingflthat;ftheynegative itolerance limit hasbeen exceeded. i @This '.:occursginstead of contact .a-im 1387 connecting itc contact 39! and .supplying-power to light 131i 3,-asnwasrthe case Awhen the volume ,offthe,esainplefeylinder head 53 was too great to Ane fthetolerance limits desired.

If switch i353 is inthe automatic position, contact arm CA will stay 'inf-itszlast-mentioned position, due to the fact that rcontactlSHis fnot connectedto lcontact armste, .and consequently plied izorelay Vcoil l312 5 .5 Unless relayeoil has a potential impressed across it,.eontact arm'CA cannotmove.

After the volume ,.difterencecn-meter13M has been' noted, a switch diillftli'ig; I8l, whichvieanfbe designated as a resetfJ switch, ymust `vloe moved-to the right, connecting contacts #t9-and f4 H respectively to .contacts M3 and M5, before thetesting operation :of the `dev-icen1ay'-lee continued. "When contact A! Bis connectedto Contact armiimrelay coil 32? has the potential Vof-power Asupply 323 irnpressed across it. Relay 321 being thus activated, it will reset `contact arm V321 of meter 43BE to a position where it is substantially `equ'idistant.from contacts :303 vand 301,-whether contact aimgl .wasconnected with .eitherA contact susor Sil-'l'. l'lhe 'second ...andgiinal action resulting. from .the movement of .swtchjlil'i 'to the right fis that. power 1S Suppliedtolrelaycoil333`through resistor si? and contacts 4 I.I -andjAIS of switchte'i.' Thisaction will movecontactst and'335 up and power willfagainbe applied to, relay c oil`325 and Contact arm .CA oistepper switch B can vcontinue moving .C1ockwise...`If switch" I.39.'is in .the..manual positionfit will haveto'hernoved to the oir positionand .thenbacli toV thev fmanual ,position to movecontactarmjCA to anadjacent clockwise position.

Thus, the embodimentiof Figs. 2-8 will either manually .Gr..automatically compare eachof the vunknown volumes oisample cavities 5 3 in Vsequence .to theknown volume' of the. master cavity Blandindicatethe volumes of eachjo'f the unknown cavitiesj'53as.agfunctionof the difference in .volume.betweenmastencavity .5i and the par- .ticular .cavity '.53 being. tested." in addition to indicating the volumeof `the cavityby meter 3ft-33, meter ',30'5 .may 'be .iagiiusted'by means iof .potentiometer I 5 tofanydesre'd'tolerance limits, either plus-or minus, and cause either light 3 is ors Ii to be illuminated, .indicating when either tolerance limit'has been exceeded. Means are Vprovided in unit` G.'forcausing`all .movement of the stepper switch unitfBto cease Whenever tolerance limits are exceeded, and'other. means .are .provided in unit' C for indicating whicho 'the Ycavities '-53 is under test .at any time.

' llt is .to rbenoted that in this .embodiment ambient .temperature and humidity changes do .not affect 'the .accuracy "of measurement because the master cavity/T5] isalways. beingcomparefl simultaneously/ with any one of. thecavities ".53 under test, .and as. cavities .53 y.are always in proximity with. cavity 5 I vany changes external conditions will effect themalhsulostantially equally. .,Thus, .the apparatusand scheme ,of .the embodiment of Figs. 2-3 is V.automatically..self-compensating as toambient. temperature and humidity variations.

.However,..such simultaneous comparison .is not .necessary .toobtain a high .degree .of accuracy of volumetriemeasurexnent. Other embodiments of the` present invention are. described hereinafter .which donotrennire simultaneous comparison of a standard ,or master cavity ,and an Yunln'iown cavi-ty. Such .embodiments `preferably. have some `means.ofmaintaining. the temperature of the air mass. within .the throat substantially. constant .Insuch embodiments, l,the volume .of the cavities heingtested maybe indicated .by `means which` is initially .calibrated andchecked .at infrequent intervals with. a standardormaster cavity. The .volumetric uni-ts of..measurement lof such indieating meansmay .be ealibratedleither in `ansolute volumeunits orina-mits which .indicate adit ference from some predeterminedstandard which is .represented .as..-izero.on. the. indicating means.

Fiss. Slzjllustrate one ,such embodiment.

.Referring-novnmo particularly to Fig. .9, nu-

meral 423' indicates a cavity .the volumeyfof .which istobe determined. A transducer A25-is mounted extremity. ".t-{hethroat tiiis, in acoustic` com mnnic'ation :withthenaviti i123.. The .transducer ^llfiand a microphone 1433 are mounted for conu an automatic gain control unit I, an amplifier unit J, a phase shifting network unit K, and an amplifier unit L. One output of amplifier L is electrically connected through wires 439 and 44| to the transducer 425. A second output or" amplifier L is connected to the automatic gain control unit I by means of two wires 443 and 445. A third output of amplifier L is connected to a frequency discriminator unit N by means of wires 441, 449, 45| and 453. The output of frequency discriminator N is fed to an indicator unit O. A power supply M supplies power to the units I-I, I, J and L. A power supply P provides a source of direct current for the indicator unit O'.

Referring now to Fig. 10 the detailed electronic circuits of the units H, I, J, K, L and M are shown. The wires 435 and 431 connect the microphone 433 to the grid circuit of a vacuum tube 455. The circuit elements of tube 455 include a grid resistor 451, a cathode resistor 459, a plate load resistor 46|, a decoupling condenser 463 and a decoupling resistor 465. A coupling condenser 461 interconnects the plate circuit of tube 455 to a second amplier tube 469. The circuit elements of tube 469 include a grid resistor 41|, a cathode resistor 413, a cathode bypass condenser 415, a decoupling condenser 411, a plate load resistor 419 and a decoupling resistor 48|. The plate circuit of tube 469 is interconnected by means of a feed-back circuit including a resistor 482 and condenser 483 to the cathode circuit of tube 455. A coupling condenser 485 interconnects the output of the amplifier unit I-I to the automatic gain control unit I. The unit I includes a duo-diode tube 491 and its associated circuit elements, namely, two coupling resistors 489 and 49|, two load resistors 493 and 495, two bleeder resistors 491 and 499, a lter condenser 50|, two oy-pass condensers 503 and 505, and a series resistor 506.

A coupling condenser 501 interconnects the automatic gain control unit I and the ampliiier unit J. The latter unit includes a vacuum tube 509 together with its associated circuit elements including a grid resistor 5| I, a cathode resistor 5|3, a decoupling condenser 5|5, a plate load resistor 5I1 and a decoupling resistor 5|9. The plate circuit of tube 509 is interconnected to the grid circuit of a vacuum tube 52| by means of a coupling condenser 523. The circuit elements of tube 52| include a grid resistor 524, a cathode ley-pass condenser 525, a cathode resistor 521, a decoupling condenser 529, a plate load resistor 53| and a decoupling resistor 533. A regenerative feed back circuit is provided between the plate of tube 52| and the cathode of tube 509 including a condenser 535 and a resistor 531. The output of the amplifier unit J is interconnected to the phase shifting network K by means of a coupling condenser 539.

The circuit elements of the phase shifting network K include three series resistors 54|, 543 and 545, a series potentiometer 541 and three condensers 549, 55| and 553.

A wire 555 interconnects the phase shifting network unit K with the grid of a vacuum tube 551 of ampliiier unit L. The circuit components of the amplifier unit L include a cathode resistor 559, a decoupling condenser 56|, a plate load resistor 563, and a decoupling resistor 565. The plate circuit of tube 551 is coupled by a condenser 566 to the grid of a power pentode tube 561. The circuit elements of the tube 561 include a cathode by-pass condenser 569, a cathode resistor 51|, a screen by-pass condenser 513, a

resistor 515 and the primary 511 of an output transformer 519. The transformer 519 has four secondaries 58|, 583, 585 and 581. The secondary 581 of transformer 519 is connected by means of wires 439 and 44| to the transducer425. A regenerative feed-back circuit including a resistor 59| is provided between this secondary 53? and the cathode of tube 551. The secondary 585 supplies a bridge rectifier unit 599 which in turn, through wires 443 and 445 supplies a D. C. control potential to the automatic gain control unit I.

The power supply M includes a transformer 593, and a duo-diode rectiiier tube 595 connected in a full wave rectifier circuit. A secondary winding 591 of transformer 593 supplies the heaters of all of the tubes in the units I-I, I, J, K, L and M. The power supply M includes a pi ilter network including a choke 599, two filter condensers 60| and 603 and a resistor 695. Two voltage regulator tubes 601 and 699 are series connected to provide different voltage-regulated potentials for the component units shown in Fig. l0. The primary of transformer 593 is energized from any suitable A. C. source L|, L-Z through a series fuse 6|| and through the internal contacts of the voltage regulator tubes 601 and 609 so that when either of these tubes is removed from its socket the primary circuit of transformer 593 will be broken.

The transducer throat 43| is provided with a heating element 6|3 the temperature of which is controlled by an internal thermostat unit 6|5 so as to maintain the temperature of throat 43| substantially constant. The power for this heater unit 613 is supplied by means of a transformer 6|1 from power source L-|, L-2.

Any ambient noise will energize the microphone 433 to cause an electronic impulse to be transmitted to the ampliiier unit H. The amplined signal will be conducted to the automatic gain control unit I which wil1 maintain the amplitude of such ampliiied signal substantially constant. The output signal of the automatic gain control unit I is cascaded into the amplifier unit J, amplified, and transmitted to the phase shifting network K. The function of unit K is to provide the correct phase relationship between the period of resonance of the cavity 423 and the phase shift through the electronic circuits of the units H, I, J and L. The potentiometer 541 of unit K (Fig. 10) provides means for adjusting this phase shift. The phase-shifted and amplified signal from unit K is transmitted to the amplifier unit L, the amplified output of which is conducted to the transducer 425 by means of wires 439 and 44|. The electrical energization of the transducer 425 will cause mechanical vibration of its diaphragm and compression and expansion in the air contained in the housing 421, which in turn will cause the mass of air contained in the throat 43| to oscillate. This air movement will acoustically energize the air contained in the cavity 423. Thus, an oscillatory electronic circuit is set up through units H, I, J, K and L which will serve to sustain an acoustic oscillation in the cavity 423, the frequency of the acoustic and electronic oscillations being a function of the diameter and the length of the throat 43| and the volume of the cavity 423. The' amplitude of these oscillations is maintained substantially constant by the action of the automatic gain control unit I. Thus, the electronic output of the amplifier unit L from the two secondaries 58| and 593 is an A. C. Wave of substantially constant amplitude, the frequency of which is a functionof the volume of the cavity 423.

As shown in Fig. 9, the output of the amplifier L is connected to the frequency discriminator unit N, the detailed circuitV arrangement of which will be described. The output of the frequency discriminator N is a D. C. signal, the potential Vof which is dependent upon the frequency of the oscillation supplied to the frequency discriminator unit N from the amplifier unit L. The output of the frequency discriminator unit N is fed to the indicator unit O which includes a galvanometer 619 (Fig.- 11) for indicating the volume of the cavity 423 being tested.

The apparatus is. calibrated by applying the throat 43| to a master cavity of known volume, causing it to resonate at its natural resonant -frequency, and adjusting indicator O for a .de-

sired reading, usually a zero reading, in accordance `with this frequency. Thereafter, thevolurne-of a sample cavity may be determined by applying the throat 43| to this cavity, causing it-to resonate, and noting the reading of the indicator O as a measurement of cavity volume, Since the temperature of the throat is maintained constant, the apparatus is substantially unaffected by differences of ambient temperature variations at the time of calibration and the time of testing the sample.

#Referring now more particularly to Fig. 11,

wherein the circuitdetails of the frequency discriminator unit N,the indicator unitlOand the power supply unit Pl are illustrated, unit N is shown to be .provided with two pairsl ofinput wires, wiresz441 and 443, and wires 454 and 453.

The former pair of wires is connected to the transformer winding 56| and the latter pair of wires is connected Yto the transformer winding 583.. One input circuit of discriminator unit N fedby wires 441 and 449 includes a potentiometer 6|9. the adjustable arm of which is connected to four paralleled condensers 62|, 623, 625 and 621. One side of the potentiometer 6|9 is connected to a choke 629 which is series connected with a condenser 63| and a dry rectifier 633. A resistor 635 is connected in parallel with condenser 63|. i.

A similar arrangement of circuit elements 1s provided for the input circuit of discriminator N fed by wires 45| and 453. This circuit includes a potentiometer 631 the adjustable arm of which is'connected to ,four paralleled condensers 639, 64|, 643 and 645. A choke 641 isv series connected with a dry rectifier 649, condenser 65| and resistor 653. and 449 is Aconnected in series with the circuit fed .by the wires 45| and 453 by a wire 655. vThe electrical output of discriminator unit N is impressed, across wires 651 and 659, wire 659 being lor-passed by a condenser 66|.

The D. C. output of the discriminator unit N is transmitted to the indicator unit O by means of wire 651.y The input circuit of unit O; is provided With a switch 663 and a series resistor 665. Two pentode tubes 661 and .669 which are connected in a modified push-pull arrangement are included in the circuit of unit O. These tubes 667 and 669 are provided with cathode resistors 61| and 613, respectively, as well as with a `common cathode resistor 615. A condenser 611 lis connected between the grid circuit 0i tube661 and the common cathode resistor 615.` A gal. vanometer 619 of the DArsonval movement, microammeter type is connected ina series, cir-1 cuit with a resistor 66| and a potentiometer, This seriesA circuit is connected between the The circuit fed by the wires 441 n plate and the screen grid of tube 661 and the plate and screen grid of tube 669. Also connected between the plate and screen grid of tube 661 and the plate and screen grid of tube 669 are two resistor 685 and 681 series connected with a potentiometer 689. The adjustable arm of vpotentiometer 689 and the common cathode resistor 615 are connected by two wires 69| and 693 respectively to the power supply unit P. Power supply unit P includes a multiwinding power transformer 695 the primary of which is powered from any suitable A. C. source L-I, L-2. A duodiode vacuum tube 691 is connected in a full-wave rectier circuit, the D. C. output of which is ltered by means of a lter network including condensers 699 and 19| and resistors 193 and 165. A voltage regulator tube 101 is connected across the D. C. output of this filter network. Connected in parallel with the voltage. regulator tube 191 are three series connected resistors 109, 1| and 1|3. 'Similarly con-'- nected in parallel with the voltage regulator tube 161 are two resistors 1|5 and 1|1 and a potentiometer 1| 9, the adjustable arm of which connects to the discriminator unit N through wire 659. The connection between resistors 1|| and 1|3 is grounded.

The operation of the discriminator unit N, the indicator unit O and the power supply unit P'is as follows:

The alternating current outputs of transformerwindings 56| and 563 (see Fig. 10) are supplied by the pair of wires 441 and 449 and the pair of wires 45| and 453 to the potentiometers 6|6 and 631, respectively. The frequency of these A. C. outputs is dependent upon the volume of the cavity 423 being'measured. The action of the circuit elements associated with potentiometer 6|9 (elements B2i-635) transforms the -alternating current input across the terminals of the potentiometer 6|9 into a D. C, potential which is impressed across the wires 655'and 659. The rectified D. C. output of the circuit elements associated with the potentiometer 631 (elements 639-653) is impressed across the wires 655 and 651 as a second D. C. potential. These two D. C. potentials are series connected by means of wire 655 and thus cause a potential to be impressed between wires 651 and 659, which D. C. potential is a function of the volume of the cavity 423 being measured.

The D. C. potential of wire 651 is impressed through the switch 663 and the resistor 665 upon the grid of tube 661 of the indicator unit O. The D. C. potential level transmitted to the control grid of the tube 661 will determine the current which will i-low through the galvanometer 619 as the control grid of tube 669 is connected directly to ground. Thus, the reading of the galvanometer 619 is dependent upon the Dg C. potential level impressed upon the grid of tube 661. Adjustments of the discriminator unitY N, the indicator unit O and the power supply unit P are made as follows:

.To eliminate any effect due to the particular characteristics of either tube 661 or tube 669, the armof switch 663 is rotated until resistor 665 is grounded. Then with the adjustable arm of potentiometer 663 at its upper limit,lthe potentiometer 689is adjusted until the galvanomy Y eter 619 is centered at zero.

, VThe potentiometers 6|9 and 631 are then adiusted so that the total and relative percentages of the outputs of windings 58| and 563 of the 

